I can't install CrowdRender or any other add on in Blender
G'day Daniel, The install function in blender just copies the addon files to your scripts/addons folder for the version of Blender that you install the addons from. So there are somethings we'd like to check.

1st is the addon actually installed into the correct directory? You will need to check your addons folder for the version of blender you are using. This location depends on your settings, but usually it will be on a path in your user directory. Mine is

~/Library/Application Support/Blender/2.81/scripts/addons/crowdrender - for mac
~/AppData/Blender Foundation/Blender/2.81/scripts/addons/crowdrender - for win
~/.config/blender/2.81/scripts/addons/crowdrender - for linux.

Check that you have a folder in addons called 'crowdrender'

If you do and it still doesn't work, can you try opening a console and running blender from it. When you try to list your addons, or enable or install the addon, any errors will be printed to the console, you can post them in response to this answer as comments. 

Alternatively, you can actually post in our forum and ask for help there since we support the crowd render addon. Asking here on stack exchange will take longer since I don't really come here that often!

Forum is at www.crowd-render.com/forum-1

All the best and look forward to hearing from you soon :)